This invention relates generally to power generation facilities, and more specifically to a method of measuring an expansion efficiency of a turbine utilized in a power plant.
At least some known power plants include a low pressure steam turbine (LP) coupled with an intermediate pressure (IP) and/or high pressure (HP) steam turbine to drive a common generator. Measuring the steam turbine efficiency, i.e. a ratio of a measured enthalpy drop to an ideal (isentropic) enthalpy drop, of the LP steam turbine may be problematic when steam entering a condenser includes a mixture of saturated steam and water. Furthermore, accurately quantifying the quality and the enthalpy of steam in a wet region of the steam flow may also problematic.
Steam turbine section expansion efficiency is commonly measured when the expansion takes place entirely in a dry or superheated region because, in the case of superheated steam, the measured temperature and pressure expressly defines steam enthalpy. The expansion efficiency of an LP steam turbine section is normally not measured in the wet region since enthalpy is no longer only a function of pressure and temperature, but is also a function of a steam moisture content. Exhaust moisture is extremely difficult to measure, and as such exhaust moisture and LP steam turbine expansion efficiency, are typically calculated by measuring other quantities and performing an energy balance calculation. Although the HP turbine and IP turbine efficiency may be directly measured, by virtue of their superheated exhausts, the uncertainty in these measurements and in the HP, IP, and LP steam turbine flow results in undesirably high uncertainty in LP power output and derived efficiency.